8,094 research outputs found
Nevanlinna-Pick interpolation by rational functions with a single pole inside the unit disk
We devise an efficient algorithm that, given points z1, . . . , zk in the open unit disk D and
a set of complex numbers {fi,0, fi,1, . . . , fi,niâ1} assigned to each zi
, produces a rational
function f with a single (multiple) pole in D, such that f is bounded on the unit circle by a
predetermined positive number, and its Taylor expansion at zi has fi,0, fi,1, . . . , fi,niâ1 as its
first ni coefficients
Assessing Research Collaboration through Co-authorship Network Analysis
This is the final version. Available from Society of Research Administrators International via the link in this recordMaterial used with permission from Society of Research Administrators InternationalInterdisciplinary research collaboration is needed to perform transformative science and accelerate innovation. The Science of Team Science strives to investigate, evaluate, and foster team science, including institutional policies that may promote or hinder collaborative interdisciplinary research and the resources and infrastructure needed to promote team science within and across institutions. Social network analysis (SNA) has emerged as a useful method to measure interdisciplinary science through the evaluation of several types of collaboration networks, including co-authorship networks. Likewise, research administrators are responsible for conducting rigorous evaluation of policies and initiatives. Within this paper, we present a case study using SNA to evaluate interprogrammatic collaboration (evidenced by co-authoring scientific papers) from 2007-2014 among scientists who are members of four formal research programs at an NCI-designated Cancer Center, the Markey Cancer Center (MCC) at the University of Kentucky. We evaluate change in network descriptives over time and implement separable temporal exponential-family random graph models (STERGMs) to estimate the effect of author and network variables on the tendency to form a co-authorship tie. We measure the diversity of the articles published over time (Blau's Index) to understand whether the changes in the co-authorship network are reflected in the diversity of articles published by research members. Over the 8-year period, we found increased inter-programmatic collaboration among research members as evidenced by co-authorship of published scientific papers. Over time, MCC Members collaborated more with others outside of their research program and outside their initial dense co-authorship groups, however tie formation continues to be driven by co-authoring with individuals of the same research program and academic department. Papers increased in diversity over time on all measures with the exception of author gender. This inter-programmatic research was fostered by policy changes in cancer center administration encouraging interdisciplinary research through both informal (e.g., annual retreats, seminar series) and formal (e.g., requiring investigators from more than two research programs on applications for pilot funding) means. Within this cancer center, interdisciplinary co-authorship increased over time as policies encouraging this collaboration were implemented. Yet, there is room for improvement in creating more interdisciplinary and diverse ties between research program members.This research was supported by the Research Communications Office as well as the Biostatistics
and Bioinformatics and the Cancer Research Informatics Shared Resources of the University
of Kentucky Markey Cancer Center, funded by the National Cancer Institute Cancer Center
Support Grant (P30CA177558). Dr. Eddensâ contribution was supported in part by a Building
Interdisciplinary Research Careers in Womenâs Health grant (#K12 DA035150) from the Office of
Womenâs Health Research, administered by the Department of Obstetrics and Gynecology of the
College of Medicine, University of Kentucky. Dr. Vanderford is supported
by the University of Kentuckyâs Cancer Center Support Grant (NCI P30CA177558) and the
Center for Cancer and Metabolism (NIGMS P20GM121327)
A semi-Markov model for stroke with piecewise-constant hazards in the presence of left, right and interval censoring.
This paper presents a parametric method of fitting semi-Markov models with piecewise-constant hazards in the presence of left, right and interval censoring. We investigate transition intensities in a three-state illness-death model with no recovery. We relax the Markov assumption by adjusting the intensity for the transition from state 2 (illness) to state 3 (death) for the time spent in state 2 through a time-varying covariate. This involves the exact time of the transition from state 1 (healthy) to state 2. When the data are subject to left or interval censoring, this time is unknown. In the estimation of the likelihood, we take into account interval censoring by integrating out all possible times for the transition from state 1 to state 2. For left censoring, we use an Expectation-Maximisation inspired algorithm. A simulation study reflects the performance of the method. The proposed combination of statistical procedures provides great flexibility. We illustrate the method in an application by using data on stroke onset for the older population from the UK Medical Research Council Cognitive Function and Ageing Study
Interictal epileptiform discharges have an independent association with cognitive impairment in children with lesional epilepsy
OBJECTIVES: The relative contribution of interictal epileptiform discharges (IEDs) to cognitive dysfunction in comparison with the underlying brain pathology is not yet understood in children with lesional focal epilepsy. METHODS: The current study investigated the association of IEDs with intellectual functioning in 103 children with medication-resistant focal epilepsy. Hierarchical multiple regression analyses were used to determine the independent contribution of IED features on intellectual functioning, after controlling for effects of lesional pathology, epilepsy duration, and medication. Exploratory analyses were conducted for language and memory scores as well as academic skills available in a subset of participants. RESULTS: The results reveal that IEDs have a negative association with IQ with independent, additive effects documented for frequent and bilaterally distributed IEDs as well as discharge enhancement in sleep. Left-lateralized IEDs had a prominent effect on verbal intelligence, in excess of the influence of left-sided brain pathology. These effects extended to other cognitive functions, most prominently for sleep-enhanced IEDs to be associated with deficits in expressive and receptive language, reading, spelling and numerical skills. SIGNIFICANCE: Overall, IED effects on cognition were of a magnitude similar to lesional influences or drug effects (topiramate use). This study demonstrates an association between IEDs and cognitive dysfunction, independent of the underlying focal brain pathology
Deposition of tin oxide, iridium and iridium oxide films by metal-organic chemical vapor deposition for electrochemical wastewater treatment
In this research, the specific electrodes were prepared by metal-organic chemical vapor deposition (MOCVD) in a hot-wall CVD reactor with the presence of O2 under reduced pressure. The Ir protective layer was deposited by using (Methylcyclopentadienyl) (1,5-cyclooctadiene) iridium (I), (MeCp)Ir(COD), as precursor. Tetraethyltin (TET) was used as precursor for the deposition of SnO2 active layer. The optimum condition for Ir film deposition was at 300 °C, 125 of O2/(MeCp)Ir(COD) molar ratio and 12 Torr of total pressure. While that of SnO2 active layer was at 380 °C, 1200 of O2/TET molar ratio and 15 Torr of total pressure. The prepared SnO2/Ir/Ti electrodes were tested for anodic oxidation of organic pollutant in a simple three-electrode electrochemical reactor using oxalic acid as model solution. The electrochemical experiments indicate that more than 80% of organic pollutant was removed after 2.1 Ah/L of charge has been applied. The kinetic investigation gives a two-step process for organic pollutant degradation, the kinetic was zero-order and first-order with respect to TOC of model solution for high and low TOC concentrations, respectively
Safe uses of Hill's model: an exact comparison with the Adair-Klotz model
<p>Abstract</p> <p>Background</p> <p>The Hill function and the related Hill model are used frequently to study processes in the living cell. There are very few studies investigating the situations in which the model can be safely used. For example, it has been shown, at the mean field level, that the dose response curve obtained from a Hill model agrees well with the dose response curves obtained from a more complicated Adair-Klotz model, provided that the parameters of the Adair-Klotz model describe strongly cooperative binding. However, it has not been established whether such findings can be extended to other properties and non-mean field (stochastic) versions of the same, or other, models.</p> <p>Results</p> <p>In this work a rather generic quantitative framework for approaching such a problem is suggested. The main idea is to focus on comparing the particle number distribution functions for Hill's and Adair-Klotz's models instead of investigating a particular property (e.g. the dose response curve). The approach is valid for any model that can be mathematically related to the Hill model. The Adair-Klotz model is used to illustrate the technique. One main and two auxiliary similarity measures were introduced to compare the distributions in a quantitative way. Both time dependent and the equilibrium properties of the similarity measures were studied.</p> <p>Conclusions</p> <p>A strongly cooperative Adair-Klotz model can be replaced by a suitable Hill model in such a way that any property computed from the two models, even the one describing stochastic features, is approximately the same. The quantitative analysis showed that boundaries of the regions in the parameter space where the models behave in the same way exhibit a rather rich structure.</p
Theoretical Models of Sunspot Structure and Dynamics
Recent progress in theoretical modeling of a sunspot is reviewed. The
observed properties of umbral dots are well reproduced by realistic simulations
of magnetoconvection in a vertical, monolithic magnetic field. To understand
the penumbra, it is useful to distinguish between the inner penumbra, dominated
by bright filaments containing slender dark cores, and the outer penumbra, made
up of dark and bright filaments of comparable width with corresponding magnetic
fields differing in inclination by some 30 degrees and strong Evershed flows in
the dark filaments along nearly horizontal or downward-plunging magnetic
fields. The role of magnetic flux pumping in submerging magnetic flux in the
outer penumbra is examined through numerical experiments, and different
geometric models of the penumbral magnetic field are discussed in the light of
high-resolution observations. Recent, realistic numerical MHD simulations of an
entire sunspot have succeeded in reproducing the salient features of the
convective pattern in the umbra and the inner penumbra. The siphon-flow
mechanism still provides the best explanation of the Evershed flow,
particularly in the outer penumbra where it often consists of cool, supersonic
downflows.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
The Evershed Effect with SOT/Hinode
The Solar Optical Telescope onboard Hinode revealed the fine-scale structure
of the Evershed flow and its relation to the filamentary structures of the
sunspot penumbra. The Evershed flow is confined in narrow channels with nearly
horizontal magnetic fields, embedded in a deep layer of the penumbral
atmosphere. It is a dynamic phenomenon with flow velocity close to the
photospheric sound speed. Individual flow channels are associated with tiny
upflows of hot gas (sources) at the inner end and downflows (sinks) at the
outer end. SOT/Hinode also discovered ``twisting'' motions of penumbral
filaments, which may be attributed to the convective nature of the Evershed
flow. The Evershed effect may be understood as a natural consequence of thermal
convection under a strong, inclined magnetic field. Current penumbral models
are discussed in the lights of these new Hinode observations.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Holographic Roberge-Weiss Transitions
We investigate N=4 SYM coupled to fundamental flavours at nonzero imaginary
quark chemical potential in the strong coupling and large N limit, using
gauge/gravity duality applied to the D3-D7 system, treating flavours in the
probe approximation. The interplay between Z(N) symmetry and the imaginary
chemical potential yields a series of first-order Roberge-Weiss transitions. An
additional thermal transition separates phases where quarks are bound/unbound
into mesons. This results in a set of Roberge-Weiss endpoints: we establish
that these are triple points, determine the Roberge-Weiss temperature, give the
curvature of the phase boundaries and confirm that the theory is analytic in
mu^2 when mu^2~0.Comment: 37 pages, 13 figures; minor comments added, to appear in JHE
- âŠ